Aluminum anodizing is an electrochemical process technology which imparts an abrasion and corrosion resistant oxide coating to aluminum and its alloys. Oxide layers formed at high current are relatively hard and are generally referred to as hard coat. Low-temperature hard anodizing produces a black coating that is desirable for many applications, including non-stick cookware. Hard coat is also used in many applications calling for abrasion and corrosion resistance, including vehicle and machine parts, laptop cases, surgical cases and structural materials.
In addition, anodized aluminum may be dyed and sealed or further treated. For example, the MICRALOX process available from Katandin may be used on surgical cases. This process is understood to include a dying step, nickel acetate seal and a final proprietary step that imparts high chemical resistance. The treated coating appears to contain metallic nickel particles produced in the nickel acetate seal. However, these coatings may not be suitable for cookware as they contain dye and nickel.
Aluminum is an amphoteric metal, meaning that the metal and its oxides dissolve much more rapidly in high and low pH solutions than in neutral solutions. Cleaning solutions like those used in dish washers and autoclaves are alkaline, high pH liquids. Accordingly, there remains room for improved anodized coatings that can survive relatively high pH treatments, relatively low pH treatments and combinations thereof over many cycles.